System responsive to the displacement of metallic objects



A. MALAQUIN SYSTEM RESPONSIVE TO THE DISPLACEMENT OF METALLIC OBJECTS Filed larch 4,-1960 I Oct. 5, 1965 s Shets-Sh'eet 1 Oct. '5, 19 65 A. MALAQUIN 3,210,539

' SYSTEM RESPONSIVE TO THE DISPLACEMENT- 0F METALLIC OBJECTS Filed March 4, 1960 $04 In 0. mu:-

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5 Sheets-Sheet 2 Oct. 5, 1965 A. MALAQUIN SYSTEM RESPONSIVE TO THE DISPLACEMENT OF METALLIC OBJECTS 5 Sheets-Sheet 3 Filed llarqh 4. 1960 FIGJO n37 -vll Oct. 5, 196 5 Filed March 4, 1960 5 Sheets-Sheet 4 A. MALAQUIN r 3,210,539 SYSTEM'RESPONSIVE TO THE' DISPLACEMENT .OF METALLIC OBJECTS Oct. 5, 1965 A. MALAQUIN SYSTEM RESPONSIVE TO THE DISPLACEMENT OF METALLIC OBJECTS 5 Sheets-Sheet 5- Filed March 4. 1960 a passing train.

United States Patent Oflice 3,210 539 SYSTEM RESPONSIVE To Tl-IE DISPLACEMENT F METALLIC OBJECTS .Andr Malaquin, Neuilly-sur-Seine, France, assignor to Societe lndustrielle dc Liaisons Electriqu'es, Paris, France, a company of France Filed Mar. 4,1960, Ser. No. 12,750 Y Claims priority, application France, Mar. 6, 1959,

788,604; Feb. 22, 1960, 819,229

3 Claims. (Cl. 246-249) This invention relates to systems responsive to the displacement of metallic objects, eg, determining the position of vehicles past a predetermined area adjacent the position where such system is located. It is especially though not exclusively concerned with such systems as used in the field of railroad signalling for indicating the fact that a train is moving past a predetermined point of track.

Inthe art of railroad signals a conventional means of Patented Oct. 5,1965

relating to a modification of the invention;

FIG.9 is a perspective view of another modification;

FIG. 10 is a simplified overhead view thereof; FIG. 11 is detailed side view in section'on XI--XI FIGS. 5, 6, 7 and 8 are simplified circuit'diagrams FIG. 10;

indicating movement of a train past a point of the track I has been a mechanical treadle mounted for actuation by Such a device is mechanically com: plicated, bulky, and prone to get out of order under the strenuous conditions to which it is exposed. It is not capable per se of discriminating between trains travelling I in opposite directions, nor of indicating the velocity and or the length dimension of the moving vehicle. t

It is an object of this invention to provide an improved system of the kind specified, which will have a number of outstanding advantages over conventional systems serving comparable purposes, in that said system will be extremely compact, rugged, free of moving mechanical parts,'and therefore willbe reliable and long-lived and require but little servicing.

Another object of this invention is to provide such a system that will readily discriminate between oppositely travelling vehicles, and will be ,able to actuate different warning signals in response thereto, and which will be capable of indicating the velocity of displacement and length of the moving object where required.

It is to be understood that while the invention is of special value in connection with train signalling systems, itis not to be limited to such use since it will be broadly applicable wherever it may be desired to detect or monitor the displacement of a metallic body through a predetermined area, e.g. for monitoring the speed of a vehicle, or counting the number of vehicles travelling past a predetermined point in either direction.

The above and further objects will appear as the disclosure proceeds.

The invention, comprises a system responsive to movement of a metal body comprising energized input winding means creating a magnetic field within an area adjacent the system; output winding means positioned in said area for normally producing an electrical output in response to said field; movement of a metal body through the area effectively modifying said field so as correspond' FIG. 12 is a simplified block diagram of a complete system; t

FIG. 13 shows the circuit of the inductive detecting device disclosed in FIG. 10, and the circuitry of the free amplifier 129 or 130 represented in FIG. 12;

FIGS. 14 and 15 show the circuitry of amplifier 131 of FIG. 12;

FIGS. 16 and 17 show a modification in the circuitry of the detecting device disclosed to FIG. 13.

Attention is directedto the fact that the closed circuits of coils 107' and 108 of FIG. 16 are coupled by means of coils 217 and 218, whereas in FIG. 13 they are connected in series. In this regard, the term electrically connected in series opposition is used in the specification to refer to a single closed circuit. It is within the scopeot the invention to substitute two magnetically coupled closed circuits for the single closed circuit of the coils.

In the embodiment illustrated in FIGS. 1 to 3, the system comprises an electromagnetic transducer consisting basically of the three windings 1, 2 and 3 wound on a common E-shaped core 4 of magnetic material. The magnetic core 4 is secured to the railroad track 6 by way of a bracket 5 clamped against the side of the rail by a clamp 7. Bracket 5 further supports: a channelshaped hood or casing 8 surrounding the windings 1, 2 and 3 to protect the latter against damaging lateral impacts.

In one specific form of. construction the magnetic core 4 comprises a stack of laminated E-sheets of thin-gauge magnetic stock, the depth of the stack being e.g. about 15 mm. The side legs of the Boom may be about 15 mm. wide, while the middle leg may be about 30 mm. wide. The long leg or web of the B may be about mm. long and 15 mm. wide. The three parallel transverse projecting legs may each be about 60 mm. long. Surrounding each ofthese projecting legs is. one of the aforesaid windings, respectively 1, 2 and 3, which each may comprise 1400 turns of copper wire 25/100 mm. diameter, with the windings being about 45 mm. high. The magnetic core 4 is arranged to extend in generally parallel relationship to the rail 6, so that its vertical midplane 9 is positioned about 25 mm. from the side face of the railhead of rail 6, with the end of the side branches positioned about 5 mm. below the plane of the wheels as they ride on the track.

Input winding 1 is supplied with 1000 c.p.s. alternating voltage from an oscillation generator 11. Output winding 3 is pushed down fully over its related side 'leg of the core 4, so that such leg projects about 15 mm. beyond the upper end of said winding. Output winding 2 how-' ever, is spaced from the main web of core 4 by means of a shim or spacer 9 about 10 mm. thick, so that the leg around which winding 2 is mounted projects beyond the upper end of said winding by about 5 mm. As a result :of this arrangement, the voltage induced in output winding 2 differs substantially from that induced in output switch controlled by a relay R5, of the dual type having two oppositely acting control windings thereon. The output of amplifier 12 is fed in parallel to two relays R1 The terminals ML are connected to the input of an amplifier 12 through connections including a and R4. Relay R1 is normally energized when the voltage across terminals ML is at least equal to apredetermined idle voltage value corresponding to the dilfercnce between the voltages induced in output windings 2 and 3m the absence of any metal body in the vicinity of the system. Relay R4 is energized when the voltage across ML exceeds a different predetermined value somewhat higher than the value above which R1 is energized Shunted across relay R4 is a capacitor 13 so selected as to ensure effective operation of the relay under the action of even extremely. short energizing pulses.

When a wheel 10 of a railroad car (FIG. 2) is passing over the detector system, the output voltage across terminals ML varies in the manner generally indicated by the graph of FIG. 4. In this graph distance in centimeters is plotted in 'abscissae to either side of a zero point corresponding substantially to the vertical transverse centerplane of the input winding 1. The voltage appearing across terminals ML is plotted in ordinates in volts, an amplification factor of 70 being assumed for convenience. It will be apparent from this graph that in the absence of a metal body (in this instance wheel) passing near the system, the average voltage across ML is about volts. Assuming a wheel is approaching the device (from the left as shown in FIG. 4) it will be seen that starting with the time the wheel has passed a point about 24 cm. ahead of the device, as measured from the zero point defined above to the point of contact of the wheel with the track (point A of the curve), the output voltage across ML gradually decreases to a value of about 2.25 volts as said distance is about 14 cm. ahead of the device (point B of the curve) at which time the position of the wheel rim contour is that indicated by line a. Thereafter the voltage gradually increases and again attains its initial value of about 5 volts substantially at the zero point, with the wheel rim then positioned on the contour 10b (point C of'the curve). As the wheel' proceeds rightward, the-voltage then gradually increases further until it reaches about 7.2 volts as the wheel is some 16 cm.

beyond the zero point, at the position indicated by line 10c (point D of the curve). The voltage then decreases again as the wheel moves away and returns to its original average value of about 5 volts as the point of contact between the wheel and rail moves beyond about 24 cm. from the zero point (point E of the curve).

In cases where a plurality of metallic bodies are to move in sequence past the system of the invention, as will be the case with the wheels of a train, it may not be necessary, in many applications including the application to railway signalling systems, that the entire series of signals generated by the passing of each wheel, or other body, be separately detected. The circuit arrangement shown in FIG. 3 may be used in such cases, this circuit being so designed that it will operate a warning signal or the like as the leading wheel of the train moves past the system, in a predetermined direction of motion. The warning signal thus initiated will operate until such time as said leading or foremost wheel has actuated a suitable cancelling means positioned on the track some distance beyond the system. The cancelling means may comprise a conventional mechanical treadle or other conventional signal device, .or it may comprise another electromagnetic detecting system according to the invention, similar to the one described herein.

The system shown in FIG. 3 will best be understood by the following description of its operation. As a train moves past the detecting unit the direction from X to Y (rightward in the drawing), the foremost wheel of the train on reaching a point adjacent output winding 2, causes an increase in the magnetic flux through the winding. The differential output voltage across ML decreases, as indicated by the section ABC of the curve of FIG. 4 described above. Relay R1 is deenergized and its contact arm I is displaced to its lower position and completes the circuit for the alarm 14 (here shown as a bell alarm) while simultaneously energizing the lower control winding of relay R5, which thereupon acts to break the circuit connecting the output of the detecting system to the input of amplifier 12. As the wheel reaches the cancelling treadle or the like positioned beyond the track segment to be monitored, actuation of such treadle (or other means) generates a signal pulse of opposite polarity which is applied to relay R5 through leads 15, 16. Relay R5 is thus deenergized and restores the circuit connecting the input of amplifier 12 to the output of the detecting unit. The system is thus restored into its initial operative condition. In this manner the sequential passing of the wheels following the foremost wheel is made ineffective to cause repetition of the warning signal.

'Should a train be moving in the opposite direction as from Y to X, then as the leading wheel of the train moves past winding 3 the magnetic flux in this winding increases and the differential output voltage across ML rises (as shown by curve portion EDC in FIG. 4). Relay R4 is energized and its associated switch contacts reverse, thereby to energize in turn the relay R3 through the circuit shown. Relay R3 thereafter remains energized through closure of self-holding contacts FG which com plete a holding circuit through shunt resistor r. As the wheel reaches a position in line with input winding 1,

the output voltage across ML is restored to its normal level (point C of the curve in FIG. 4) and relay R4 is deenergizcd. Then as the wheel moves away from winding 3 the voltage across ML falls (section CBA of the graph) relay R1 thereupon is deenergized and its H contact is moved to the lower position completing an energjizing circuit for relay R2. As the wheel continues to move away the voltage across ML rises back to the normal value (point A on the graph). Relay R1 is now again energized, and the closure of its upper I contacts generates a pulse which is transmitted by way of the contacts I, J, F to short-circuit the winding of relay R3.

Relay R2 is delayed-operating, having a capacitor 17 connected across its winding, so that its J contacts remain closed for a sufficient interval of time after the energizing circuit for said relay has been opened at the H-contacts of relay R1, to enable the afore-mentioned pulse to pass for shorting the relay R3. Relay R3 on thus being shorted becomes deenergized and the system is thus restored to its ready or standby condition. It will be noted that in the event the train is moving from Y. toward X, the warning signal 14 is not operated. If desired, another alarm signal, preferably of different character, e.g., a bell of different pitch, from the alarm 14, may be provided and so connected as to be operated for example on closure of the upper K contacts on energization of the relay R3.

In the circuit diagram of FIG. 3 it will be observed tljat any fault occurring in the system, such as a breakdown of the oscillation generator, a break in any connecting wire, or the like, will result in deenergizing the relay R1, which in turn will be manifested as a sounding of the alarm 14, thus ensuring fail-safe operation.

In the system shown in FIGS. 5, 6, 7 and 8, the output windings 2 and 3 both having equal numbers of turns are wound in opposing relationship and are arranged at equal. distances on opposite sides from input winding 1. The said windings have no magnetic cores associated with them. Winding 1 is supplied with current from the output of an oscillation generator 11, at a frequency of, say, 2,000 c.p.s. Output windings 2 and 3 normally have different magnetic fluxes therein due to the provision of a magnetic armature 18 arranged nearer winding 3 than winding 2. Windings 2 and 3 are connected in series-opposition, so that a differential voltage equal to the difference between the voltages induced in them appears across output terminals LM.

In the absence of a metal body adjacent the system, as in FIG. 5, input winding 1 induces a smaller voltage in output winding 2 and a greater voltage in winding 3 the body 19 is exerting owing to the presence of thc additional flux lines generatcd by armature 18. The resulting differential output voltage appearing across terminals LM corresponds to the average potential (e.g. 5 v.) present at any one of the points A, C, E in the graph of FIG. 4.

When a metal body 19 is moving past winding 2 (FIG. 6) the flux in this winding increases, increasing the induced voltage .in the winding and thereby decreasing the differential voltage outputacross LM (as in section AB ofthe graph, FIG. 4). The output approaches zero or may even change in polarity, depending on the relative size-of the body 19 as compared to the armature 18.

The output voltage induced in winding 2 then falls off until the body 19 reaches a position adjacent winding 3 (FIG. 7) while still substantially overlying the winding 2. At this time the net output voltage across LM is substantially, restored to its initial value (as at the point C, FIG. 4) and retains this value throughout the time equal magnetic effects on both windings 2 and 3. i j

After the body 19 has moved beyond winding 2 while still remaining close to winding 3 (as in FIG. 8) the output voltage across LM increasesfand rises above its average value (as in the section CDE of the curve, FIG. 4) since the flux in winding 3 is now greater than the normal value due to the presence of the body 19 which creates additional'fiux in excess of the flux created by the armature 18 alone as in the condition of FIG. 5.

Finally when the metal body 19 has moved completely beyond the system the output voltage LM is restored to its mean level (point E in FIG.'4), the condition now being the same as in FIG. 5.

Should the metal body 19 be moving in the reverse direction, similar variations in the output across LM occur but in reverse order; that is, the output voltage first increases-while the body is approaching winding 3, then passes through its mean voltage level as the body 19' (with armature 18) is exerting equal influences on both windings, decreases as the body moves beyond winding 3 but remains near the winding 2, and resumes its initial level when the body 19 has moved completely beyond the device.

It will be seen that with the system described, electromotive forces induced in the secondary windings 2 and 3 are unbalanced in the absence of body 19 so that a control .current providing an output voltage of substantially constant value will be fed from the secondary windings.

The body 19 tends to balance said electromotive forces as it approaches winding 2, or to increase the unbalance of said forces as it approaches winding 3. The output voltage-therefore. will decrease below and return to its constant value when body 19 moves towards or from winding 1 over winding 2 (see phase A-B-C in FIG. 4), or will increase above and return to its constant value when body 19 moves towards or from winding 1 over winding 3 (see phase C-D-E in FIG. 4), such variations in output voltage of the control current provide two distinct signals whereby measurements of the time interval between the two signals (as between A and E, or B and D, FIG. 4) will provide an indication of the length dimension of the moving body if its velocity is known, or conversely an indication of its velocity if its length is known.

Generally similar results may be obtained by simply measuring the time duration of a single unidirectionab voltage surge i.e. the time of influence of the body upon a single one of the windings 2 or 3 (as between points A and C, or points C and E in FIG. 4).

By measuring the lapse of time from the initial point of a unidirectional variation in voltage (as from point A) to the point at which the voltage has reached its peak value (as at point B), it is easier to measure the rate of displacement of a metal body of unknown or indeterminate length dimension, provided its length dimension in the direction of displacement is greaterthan the distance from an output winding to the input winding of the required for this purpose may readily be effected by a variety of conventional means, generally electronic in character.

Various changes may of course be introduced in the forms of embodiment described above and illustrated,

without exceeding the scope of the invention. Thus, the form of transducer device used may be varied considerably from that shown. For example both output windings may be positioned to the same side from the input winding rather than to opposite sides of it. The important thing is that both the output windings should be positioned simultaneously within the range of influence, or field, created by the input winding and within the range of influence, or field, introduced by movement of at least part of the metal mass to be detected. The field is not necessarily a magnetic field, although the embodiments shown herein use magnetic fields, since equivalent results might be obtained with electromagnetic fields. In cases where it is superfluous to determine the direction of displacement, the transducer unit may be simplified so as to have only a single output winding, to which a fixed biassing voltage may be applied.

The system illustrated in FIGS. 9 to 11 comprises two spaced transducers generally designated 101 and 102, see FIG. 10. Each transducer comprises a U-shaped magnetic core 103 and 104 respectively, an input winding 105 and 106 respectively and an output winding 107 and 108. The input and output windings of each transducer are threaded over the upstanding legs of the related U-core, being generally symmetrically arranged. However, one of the transducers here designated 102, additionally includes a pair of projections 109 and 110 of magnetic material positioned at the ends of the respective legs of the U-core 104 thereof. struction the entire two-transducer unit is bodily imbedded in a mass of suitable plastic material 120 such as a polyester resin charged with silica filler material and contained in a casing made of fibre glass fabric impregnated with polyester resin. The casing has a pair of downwardly projecting extensions or tabs 111 and 112 at its ends, provided with apertures 113 and 114. Electric leads, not shown, are imbedded in the plastic mass and extend outwards through a connector 115 for connection with a cable conductor 117. The unit is attached to a side of a rail in a manner that will be apparent from FIG. 9, as by being bolted to a baseplate on a sleeper or tie of the railway track with the upper horizontal portion of the unit, containing the actual transducers, applied into close engagement with the side of the rail just below therailhead. It will be apparent'from the drawings that the transducer unit is so supported that the axes of its windings are directed at an upward and outward angle from the side of the rail. FIG. 11 further shows that the upper and outer ends of the windings are positioned a short distance below the bottom end of the flange of a wheel 118 as such wheel travels past the transducer. It will be understood that the plastic and fibreglass sealing means described and shown in connection with this embodiment provide a highly effective means of protecting the operative components of the system against atmos pheric humidity, mud, minute metal particles as shorn off the rails by the wheel, and other foreign materials as well as impacts all liable to damage the system. As will be evident a similar sealing means may if desired be applied with the other first embodiment of the invention heretofore described and shown.

In the pair of transducers 101 and 102 the electrical In the illustrated con- U-core.

outputs of both output windings are balanced against each other prior to the final plastic sealing step as by adjusting the positions of the windings upon the common The two transducers are mounted at relatively closely spaced positions along the rail (e.g. an inch or so apart) as shown'in FIG. 10, being preferably mounted upon a'common supporting plate 19 which simultaneously serves as a screen that will minimize disturbance due to stray magnetic fields.

.Prior to .the installing of the two-transducer unitalong a side of a rail, the magnetic projections 109-110 present on the assembly 102 are ineffective to introduce any unbalance between the outputs of the two assemblies when similar voltages are applied to their respective input windv ducer 101 is coupled with the adjacent portion of the rail,

so that the output voltage from 102 will then be normally higher than the output voltage from Referring to FIG. 12, there is diagrammatically shown a complete system for signalling the passing of a railway train at a predetermined point of the track. The system comprises two separate units 121 and 122, each similar to the unit shown in'FIGS. 9-11, i.e., each comprising a pair of transducers 101 and 102 each having an input and an output winding on a U-shaped core. The reason for the provision of the additional unit 122 will appear later. The system is assumed to be provided for the indication of train movement in the direction shown by arrow 124. Broadly, there is associated with each unit 121,122 a DC. supply source respectively 125, 126 for providing electric energy to the circuit components, an oscillation-generator 127, 128 energized from said source for applying A.C. voltage (at e.g. 28,000 c.p.s.) to the input windings of each transducer unit, a pre-amplifier and level-detector circuit 129, 130 respectively responsive to the output from the output windings of each unit, a common power amplifier 131, and a relay 132, operated by the amplifier output and having associated contacts .controlling the energization of a suitable bell alarm 134 or other signal from a DC. source 133.

Referring to FIG. 13, the circuit connections associated 'With one of the transducer units, e.g.,junit 121, are shown in detail. Both input windings 105, 106 of the two transducers 101 and 102 are connected in series with the aforementioned oscillator-127. The respective output windings 107, 108 each shunted by a capacitor 135, 136 are connected in series opposing relation by way of leads 137, v 139, 140 to the opposite sides of a primary 138 of a cou-- pling transformer T1. It will be understood from previous explanations that prior to erection of the system alongside a rail, adjustments. are so made that the voltages induced in output windings'l07, 108 from the related input windings 105, 106 cancel each other so that there is then no resulting output across transformer primary 138. Such adjustment is preferably carried out before the transducer assembly is sealed in its plastic mass, as by adjusting the positions of the windings on their respective cores. On the transducer unit being secured to a side of the rail, the voltage induced in winding 108 of unit 102 becomes greater than that induced in winding 107 of unit 101 owing to the presence of magnetic projections 109, 110 on the core of unit 102 which projections cooperate with the nearby steel rail to provide a more closely-coupled magnetic circuit than that associated with unit 101. A

net differential output is therefore applied to transformer T1 in the absence of any railroad car wheel travelling past the system.

The output fromtranstormer T1 is applied to a pre transistor amplifier stages in cascade.

amplifier circuit 141 shown in FIG. 13 as comprising two A first transistor 142 has its base connected to a mid-tap of the sec )ndary of transformer T1 which secondary is shunted by a tuning capacitor 144. The emitter of transistor 142 is connected for A.C. signal voltage with one end of the transformer secondary through capacitor 145 and is connected with positive biasing polarity through a parallel RC network 151-146. The collector is connected through resistor 152 to negative polarity (or ground) and through RC network 148 with the base of the second-stage transistor 143 to pass the signal thereto. The emitter of transistor 143 is positively biased by way of RC network 153-147 from positive polarity. The collector is connected to negative (or ground) polarity through series resistors 154, 155. Two outputs are derived from the pre-amplifier across the resistor 154, and are passed by way of capacitors 149 and to the respective output terminals A and B.

The output from terminal A is applied to a lower-level indicator circuit 156 (FIG. 14), and the output from terminal B is applied to a high-level indicator circuit 157.

In low-level indicator 156, the output signal from A is applied to the base of a transistor 158 also connected through resistor 173 to negative or ground potential. The emitter of 158 is positively biased through parallel RC combination 168-162. From the collector, connected to negative through resistor 172, the signal is passed through coupling capacitor 164 to the base of a second-stagetranwinding L1 of an output coupling transformer T2 having two secondaries L2 and L3. The part-secondary L3 provides the output to the common power amplifier 31, While winding L2 provides a positive'feedback connection to the base of first-stage transistor 158. For this purpose winding L2 has one end connected to positive polarity and its other end connected through rectifier 174 and resistor 166 to the adjustable tap of a potentiometer 165, shunted by capacitor and connected between positive polarity and the base of transistor 158 by way of limiting resistor 167. The cathode of diode 174 is connected to positive terminal by way of a capacitor 161.

' In the operation of the system so far described, it will be recalled that in the normal standby condition, i.e., in the absence of a train moving past the system a voltage output of predetermined fixed amplitudeis permanently applied to coupling transformer T1 (FIG, 13). This voltage is pre-ampl ified in the two-stage preamplifier 141 I and passed through terminal A to low-level indicator 156.

approaching that normally induced in output Winding 108 of unit 102, whereupon the differential signal normally present at coupling transformer T1 drops to a value approaching zero. The signal applied to primary L1 of the output transformer T2 of low-level indicator circuit 156 decreases accordingly. When the voltage induced from primary winding L1 in part-secondary L2 has dropped to an amplitude less than a predetermined level, the feedback signal applied through the diode 174 and resistors 166-165-167 to the base of transistor 158 is suppressed, and the transistor is rendered non-conductive. Thus the output from winding L3 to the power amplifier 131 is cut off sharply asthe input to transformer T1 falls becircuit 156 just described and corresponding circuit elements have been designated with the same reference numerals primed, therefore they need not be recited in detail. In circuit 157, the normal or standby signal applied through terminal B is ineffective to render transistor '158' conductive and hence such signal is not passed to the output transformer T2 of circuit 157. When however a wheel in moving past the system in the direction of arrow 124 (FIG. 12) reaches a position adjacent the transducer 102, which is the downstream transducer of the upstream unit 121, the output voltage applied to transformer T1 (FIG. 13) increases beyond its normal standby-value. The corresponding increased voltage at terminal B now renders the transistor 158' conductive and is passed thercthrough and through transistor 159' to output coupling transformer T2. The secondary winding L2 passes part of this signal as a feedback voltage to transistor 158' as in the circuit 156 previously described, but in this case part of this signal is applied through a con- .nection 175 to a storage network 176 comprising a capacitor 177 having one side connected to a positive terminal and its other side connected in series between two similarly-poled diode rectifiers 178, 179. The free terminal of diode 178 has the aforementioned signal from winding L2 applied to it and is moreover connected through a capacitor 180 to positive polarity, while the free terminal of diode 179 is connected through lead 180' to the adjustable tap of potentiometer 165 in circuit 156. Thus, on occurrence of an output voltage at winding L2 part of such voltage is stored as a charge on capacitor 177. The stored energy is later fed by Way of lead 180' and resistors 165, 167 to the base of transistor 158 in circuit 156 on discharge of storage capacitor 177 to serve a purpose that will presently appear.

Referring to FIG. which is a detailed circuit diagram of output amplifier 131 (FIG. 12), the circuit includes an input coupling transformer T4 to the primary of which the output signal from winding L3 of low-level indicator circuit 156 is normally applied. From a center tap of the secondary of T4, shunted by a tuning capacitor 193 and having one end connected to positive battery, the input signal is led by way of capacitor 194 to the emitter of a gating transistor 181. The base of 181 is connected through resistor 183 and normally-open manual switch 182 to negative polarity. The emitter is biassed through a voltage divider comprising resistor 204 connected to positive, and resistor 205 connected to negative terminal. The collector of 181 is connected to negative terminal through resistor 206. The transistor is capable of conducting current through its emitter-collector path only when its base is sufficiently negative. An initial negative bias may be applied to said base by momentary closure of switch 182. The conductive condition is thereafter maintained (so long as an input signal is present) owing to a feedback loop provided from the output of the amplifier, as will be further described, through resistor 202 and a reverse-poled diode connected to said base. The base is further connected through resistor 203 with a positive biassing polarity. When transistor 181 conducts, the signal is passed through capacitor 195 to the base of a second-stage transistor 184, which base is biassed by voltage-divider, 208409. The collector is negatively biassed through resistor 211. The emitter, positivebiassed through RC network 210-198 passes the signal through capacitor 201 to the base of a third-stage transistor 185. This base is biassed through voltage-divider 212-213. The emitter of 185 is positively biassed through RC-network 214-199. The collector passes the signal through a coupling transformer T6 to a power-amplifier stage comprising the pair of pushpull connected transistors 186, 187. The midtap of the secondary of T6 is connected to bias potential through divider resistors 215- 216. The common junction of the emitters of the pushpull transistors is connected to positive terminal through resistor 207. The output from the pushpull stage as derived across the collectors of 186, 187 is applied through an output transformer T7 to a full-Wave rectifier bridge 188, 189, 190, 191 and the rectified output therefrom is applied across the winding of relay 132 shunted by capacitor 200. Relay 132 controls energization of alarm 134 from battery 133 as previously described. The afore-mentioned feedback connection for biassing the base of transistor 181 is taken from the negative output terminal of the fullwave rectifier bridge.

After the gating transistor 181 has initially been rendered conducting by momentary closure of manual switch 182, it retains its conductive state so long as an input signal is applied to it by transformer T4 because of the feedback connection from the negative output terminal as just described, so that relay 132 remains energized and alarm device 134 remains silent. However, on the standby signal from low-level indicator 156 to transformer T4 being cut off in the manner previously explained deenergizing relay 132 and sounding the bell 134, the feedback connection no longer applies a negative bias to the base of transistor 181 and-the latter can no longer conduct. Thus, when the normal standby signal is restored at the input transformer T4 such signal remains ineffective, relay 132 remains deenergized, and bell 134 continues to-ring. The normal standby condition may be restored manually by momentarily closing switch 182. According to the invention, means are further provided for automatically applying a'cancelling signal to the amplifier 131 in order to render gating transistor 181 conductive again and terminate the action of alarm 134. g

Such cancelling means are applied by way of a second input transformer T5, having its center-tapped secondary winding, shunted by capacitor 196 and connected on one side to positive terminal. The center-tap is connected through capacitor 197 and lead 192 to the base of second-stage transistor 184. It will be apparent that in the non-conductive condition of transistor 181, should an A.-C. cancelling signal be applied to transformer T5, such signal will be amplified through the subsequent stages of 131 and result in a negative voltage being applied through the feedback loop to the base of transistor 181, thereby reinstating normal operation.

The signal to the cancelling input T5 is, in the preferred embodiment generally illustrated in FIG. 12, de-

rived from a two transducer unit similar to the one heretofore described, and mounted alongside the track beyond the first unit. This further units has been illustrated as 122 in FIG. 12, and is exactly similar to the one described with reference to FIG. 10. The signal applied to the cancelling input of amplifier 131 is derived from the output winding similar to L3 of the high level indicator circuit (similar to circuit 157, FIG. 14) of such further unit 122.

The fully-symmetrical system thus provided will be capable of discrimination between the passing of trains in either direction and of providing separate indications. For this purpose, there need simply be included a further amplifier (not shown) similar to amplifier 131, with an output relay similar to 132 controlling a further Warning device such as 134, but differing therefrom e.g. in the pitch of the sound signal produced by it. This further amplifier 131 would have its main input (such as transformer T4) supplied from the output winding corresponding to L3 of the low level indicator circuit of the further unit 122, and would have its cancelling input, corresponding to transformer T4, supplied from the output 11 winding L3 of'the high-level indicator circuit 157 of the first unit 121.

To summarize the operation of the system, assume a train is travelling rightward, per arrow 124 in FIG. 12. As the foremost wheel reaches transducer 101 of unit 121 the output of said unit decreases below its critical level and low-level indicator'circuit 156 of unit 121 cuts off the gating transistorlsl therein, whereby the bell 134 is sounded. Transistor 181 remains cut off and bell 134'k'eeps on ringing until the foremost wheel of the 'off the supply from input T5 of amplifier 131 cutting trainhas reached transducer 102 of unit 122, at which time the differential output of said unit exceeds its upper critical level and high-level indicator circuit (corresponding to 157) of said unit applies a signal to the cancelling input T5 of amplifier 131. This renders transistor 181 conductive again so that the bell 134 is disabled, provided there is no further wheel of the train moving at that time past the transducer 101 of unit 121. Otherwise relay 132 would immediately again be deenergized and there would be practically no interruption in the sounding of the bell.

Assuming next that a train is travelling in the opposite direction, then as its foremost wheel moves past the transducer corresponding. to ,102 in unit 122, the high level indicator of unit 122 generates a cancelling signal which remains ineffective on amplifier 131. As the wheel reaches transducer 102 of unit 121, the differential output from said unit increases beyond its standby level and the high-level indicator 157 of said unit applies a charge uninterrupted without causing a deenergization of relay 132 and attending cut-off of transistor 181. bell 134 is not sounded in this case.

It will be understood'that during the' above operation, the alarm corresponding to bell 134 but serving to indicate train movement in the opposite (leftward) direction would be controlled in an exactly analogous manner so as to be sounded only for leftward train movement.

It will be observed that the circuits described above utilize A.-C. amplification throughout. Thus incase of a fault or defectin any of the circuits the over-all amplification gain will drop to zero or a low value, causdeenergization of relay 132. This ensuring full fail-safe operation.

A set of numerical data will now be given as used in one practical embodiment of the system described in connection with FIGS. 9-15, it being understood that the data given are indicative only.

In each transducer, the U-core was of cylindrical cross section, 14 mm. dia, Ferroxcub material. The projections 109, 110 were square sectioned, 14 mm. to a side, made of ferrox-cub, and projected about 5 mm. towards the rail surface. Interaxial spacing between in- Thus the putand output windings was 50 mm. Between the two Capacitors:

135, 136 pf 8,000 144 5,000 145 pf 0.47

146, 147 8 148 47,000 149, 150 3,000 160, 161 gf 0.47 162, 163 8 164 pf 30,000 177 ,u.f 10 180 ;/.f 2 193 pf 5,000 194, 195, 201 ..af 0.47 196 pf 5,000 i 197 p.f 0.47 198, 199 200 nf 1 Resistors:

152 56K 153 ohms 680 166 5.6 167 7.5 168 ohms 470 169 3.3K 170 ohms 270 171 15K 172 3.3K 173 10K 183, 202 1K 203, 204, 205, 206 5K 207 c ohms.. 30 208' 160K 209 30K 210 3.9K 211 5.6K 212 68K 213 8:2K 214 ohrns 820 215 do- 100 Transistors 142, 143, 181, 184 and 185 were of the type identified as DC 7t. Transistors 186 and 187 the type 0C 72. I

FIGS. 16 and 17 illustrate a modification of the invention serving to facilitate the initial adjustment of the transducers of a system of the type described with reference to FIGS. 9l5 in order to obtain a desired value of differential output or standby voltage. This modification has the further advantage of facilitating any adjustments required in conditioning the transducers for service as for selecting the direction of train travel to which a particular unit will respond.

In this modification, the output windings 107, 108 rather constitute the split primary of a coupling transformer the secondary 219 of which is connected to input of the pre-arnplifier 141, which input is shunted by tuning capacitor 220. Any suitable means may be used for adjusting the relative coupling between windings 217-219 on the one hand, windings 218-219 on the other. Thus, FIG. 17 shows one advantageous form of coupling transformer, having a three-legged core 222. Wound around the center leg of the core is the output winding 219, and around this are wound the two split input windings 217, 218. The center leg of the core 222 has, aligned screw threaded holes formed therein in which threaded slugs 221, 223 of magnetic material are adjustably insertable to permit independent adjustment of the coupling between each primary and the common secondary windings.

It will be understood that the various embodiments of the invention described in detail herein may be modified in a variety of ways, as by transposing certain features shown in one embodiment, to a different embodiment, or by modifying the circuitry illustrated, without departing from the scope of the invention as defined by the ensuing claims.

What is claimed is:

1. A system for detecting and signalling the passage of a railway wheel comprising an inductive detecting device including primary coil means, a source of alternating current coupled to said primary coil means and two secondary coils electrically connected in series opposition and disposedalong the passage of said wheel with said primary coilmeans therebetween, said secondary coils having differentinductive relations with said primary trol current.

2. A railroad signalling system comprising a detecting device including multi-legged core means, energizable input winding means on the core means and output windings on the core means at opposite sides from the input winding means, means detachably attaching the device to a railroad track withthe windings spaced below and adjacent the upper surface of the track to cause by the passage of a wheel on said track, first an increase between the magnetic coupling between said input winding means andione of said output windings and then an increase of coil means sothat the secondary coils have induced there- 'in'in the absence of the wheel unbalanced electromotive the magnetic coupling between said input winding means and the other of said output windings thereby varying the electrical output from said output windings, an output device connected to said output windings and responsive to variations in the output thereof, and means normally increasing the magnetic coupling of said input winding means with one of said output windings whereby, said detecting device normally produces a constant output, said output device being responsive only to a predetermined variation in said output.

3. A system as claimed in claim 2, wherein said means increasing the magnetic coupling comprises a magnetic projection extending into proximity with the surface of said rail to provide, a narrower airgap therewith on one side of said core means.

References Cited by the Examiner UNITED STATES PATENTS 881,005 3/08 Kleinschmidt 246-249 1,702,997 2/29 Ewing et al 246- 2,045,923 6/36 Reichard 246-249 2,892,078 6/59 Orthuber 246-249 FOREIGN PATENTS 788,453 l/58 Great Britain.

885,866 8/53 Germany.

896,657 5/44 France.

114,728 6/57 France.

EUGENE G. BOTZ, Primary Examiner. JAMES S. SHANK, LEO QUACKENBUSH, Examiners. 

1. A SYSTEM FOR DETECTING AND SIGALLING THE PASSAGE OF A RAILWAY WHEEL COMPRISING AN INDUCTIVE DETECTING DEVICE INCLUDING PRIMARY COIL MEANS, A SOURCE OF ALTERNATING CURRENT COUPLED TO SAID PRIMARY COIL MEANS AND TWO SECONDARY COILS ELECTRICALLY CONNECTED IN SERIES OPPOSITION AND DISPOSED ALONG THE PASSAGE OF SAID WHEEL WITH SAID PRIMARY COIL MEANS THEREBETWEEN, SAID SECONDARY COILS HAVING DIFFERENT INDUCTIVE RELATIONS WITH SAID PRIMARY COIL MEANS SO THAT THE SECONDARY COILS HAVE INDUCED THEREIN IN THE ABSENCE OF THE WHEEL UNBALANCED ELECTROMOTIVE FORCES THEREBY PROVIDING A CONTROL CURRENT, SAID CONTROL CURRENT DECREASING WITH SAID WHEEL APPROACHING SAID DEVICE IN A FIRST DIRECTION AND INCREASING WITH SAID WHEEL APPROACHING SAID DEVICE IN AN OPPOSITE DIRECTION, SIGNALLING MEANS RESPONSIVE TO SAID CONTROL CURRENT FOR PRODUCING A SIGNAL WITH SAID CONTROL CURRENT DECREASED, AND MEANS RESPONISVE TO SAID CONTROL CURRENT FOR RENDERING SAID SIGNALLING MEANS INEFFECTIVEUPON INCREASE IN THE CONTROL CURRENT. 